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another question about black holes


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was wondering the other day we know that nothing can escape from a black hole not even light,but then i watched something that said black holes emit jets of radiation,how can this be if not even light can escape? is there a sweet spot in the centre that is weaker so allows the radiation to escape and if so wouldn't there be a white dot where that sweet spot is where light is managing to escape or am i barking up the completely wrong tree (which is my guess!)

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The radiation itself comes from near, but outside, the black hole. Some of the energy that drives the jets come from the rotational energy of the black hole (Blandford-Znajek mechanism).

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I think I understand Hawkins radiation, it's just the animation I have seen seems to show a beam of radiation coming from the centre of the black hole and as George stated Hawkins radiation comes from the edge of the event horizon. Thanks for all the help guys

Edited by starstalker
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I rememeber seeing a tv program where it shows the ray coming from the centre and being expelled at 90deg to the galaxy both top and bottom... I dont remember what program it was though

diagram.jpg?w=485&h=404

Edited by Keiran
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Its the radiation being emitted from the super heated gas of particles falling into the black hole. They gain a lot of energy falling in, and some of it comes out as radiation or jets of particles. The magnetic field produced means it comes out in a tight cone. This is very different to hawking radiation.

Its believe these are the power behind AGN, a blazar being one where the cone is directly lined up with our line of sight.

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Just been to a seminar on AGNs and black holes. Now understand it much better!

If its a fast growing black hole, its basically radiation pressure of light that is in balance with the infalling matter - Eddingtons limit. In this case you see a lot of luminance in the visible and higher wave bands.

For slower growing black holes, the excess energy is remove mechanically, by jets of material focused by the strong magnetic fields generated.

So that's why we see Quasar type objects - shining brightly, and others with jets that emit more in the radio spectrum. The growth rate is influenced by the age and type of galaxy.

There you go - an hours talk condensed!

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